What determines the taste and appearance of peaches? It took us 14 years to figure it out

"Ten years of exploring the secrets of peaches, ingenuity to solve problems". I am Han Yuepeng, the leader of the fruit tree molecular breeding team of Wuhan Botanical Garden, Chinese Academy of Sciences, and a post scientist of the National Peach Industry Technology System. Since 2010, my team and I have been committed to the research of peach fruit quality genetics and improvement, and it has been more than fourteen years.

Peach, originated in China, has a history of thousands of years of cultivation in my country. The earliest documented record can be traced back to the Book of Songs, "There are peaches in the garden, the fruit is delicious", "The peach trees are young and tender, and their flowers are bright and bright". Tao Yuanming of the Jin Dynasty described a paradise in "Peach Blossom Spring", an ideal society isolated from the world, peaceful and quiet. This allusion also made "Peach Blossom Spring" a synonym for an ideal world. The poem "The fragrance of April on earth is gone, and the peach blossoms in the mountain temple are in full bloom" by the Tang Dynasty poet Bai Juyi suggests that people should cherish time and seize every beautiful moment of life.

In addition, peaches are often regarded as a symbol of longevity and immortality. In the famous Taoist legend, the Queen Mother of the West's Peach Banquet was themed around peaches. Legend has it that these peaches ripen only once every few thousand years, and eating them can make one immortal. It can be seen that the small peach is not only a delicious fruit, but also occupies an important position in Chinese culture, becoming a common element in literature, art and folklore. In fact, from a biological point of view, there is a lot of knowledge behind the small peach.

Peach fruit is rich in vitamin C, cellulose and various minerals, which are good for health. Therefore, as a nutritious and delicious fruit, peach is widely demanded in the market. With the continuous progress and development of modern breeding technology, more and more peach varieties are on the market.

In terms of fruit color , there are red-fleshed peaches, yellow-fleshed peaches, and white-fleshed peaches; in terms of appearance , there are round peaches and flat peaches; according to whether there are hairs on the fruit surface, they can be divided into nectarines (smooth surface) and hairy peaches (hairy surface); according to the texture of the flesh, they can be divided into soft peaches (solute) and hard peaches (non-solute); according to the degree of separation between the pit and the flesh, there are differences between free pits and sticky pits... "The rich morphological variation shows that peaches have a high degree of genetic diversity and contain rich scientific mysteries.

Our research is trying to uncover these mysteries, help with the inheritance and improvement of peach fruit quality, and contribute to the healthy development of the peach industry ."

Part.1 "One in a thousand" to unlock the secret of blood peach coloring

Hubei is one of the main peach producing areas in my country, with a planting area of ​​about 1.1 million mu, ranking fourth among all provinces in the country, and currently showing an increasing trend year by year. Among them, the red flesh peach, a local variety in Hubei, is favored by consumers for its blood-red flesh color and high antioxidant capacity, and has also attracted great attention from breeders. Red flesh peach, also known as blood peach, according to the "Flora of China·Peach", Hubei's red flesh peach may have originally come from Dawu County. Different places have different names for red flesh peach, and it also has many names such as Dahongpao, Xiaohongpao, Yanzhitao, Zhushahong, and Gouxuetao.

After I returned to China to set up a laboratory, the first topic I was interested in was red peach. However, the laboratory conditions were simple and the funds were scarce, so it was not easy to carry out this research. Fortunately, I met a group of hardworking and adventurous graduate students. I am also very grateful to Researcher He Huaping of the Fruit and Tea Research Institute of Hubei Academy of Agricultural Sciences for enthusiastically providing us with research materials at that time.

Everything was ready, and the topic of analyzing the coloring mechanism of blood peaches was officially put on the agenda. After preliminary experiments, we obtained complex analysis results, which meant that we had to find the key gene that controls the coloring trait of blood peaches from thousands of differentially expressed candidate genes . Obviously, this was not an easy task.

During that time, my students and I spent almost every day in the laboratory, constantly optimizing experimental plans, improving experimental methods, and repeatedly consulting relevant literature and checking experimental data. Finally, in cooperation with New Zealand scientists, we used virus-mediated transient silencing technology to achieve the goal of verifying candidate genes in peach pulp.

Finally, the research team successfully cloned the BL gene that regulates the coloring of blood peaches , and successfully explained why the flesh of blood peaches and white peaches is so different. These results have become a major breakthrough for our team. At the same time, the BL gene discovered in the study is also the first functional gene discovered in the field of fruit tree research in China through map-based cloning methods . This scientific discovery has greatly promoted the genetic research of fruit trees in China.

Part.2 Red "heart" brings problems to canned food production

In addition to the special variety of blood peaches, there is another type of peach that is also common in daily life, but few people think about the scientific issues behind it. In the peach processing industry, there is a phenomenon called "near-core red", that is, the flesh close to the peach pit is red. This phenomenon brings additional challenges to the production of canned peaches. Because this means that when making canned peaches, people need to perform additional processing on the red flesh part, which increases production costs. Therefore, figuring out the cause of the "near-core red" trait is not only an interesting scientific issue, but also an industry demand that needs to be solved urgently.

Through genetics and molecular biology and other experimental techniques, we screened out dozens of possible candidate genes. Through continuous elimination and testing, we finally identified the important gene that regulates the formation of the near-core red trait of peach fruit and discovered its key synergistic factor. Under the joint action of these two genes, the transcription level of the "star gene" PpMYB10.1 that regulates anthocyanin synthesis is promoted, thereby causing a large amount of anthocyanin accumulation near the core , leading to the "near-core red" phenomenon. This research result can provide an important theoretical basis and gene resources for the selection and breeding of new processing peach varieties.

Part.3 Every peach has hairs on it, but why are nectarines smooth?

As a fruit with rich forms, peaches differ not only in their flesh but also in their appearance. People have always been curious about why some peaches have hair on the surface, while others are smooth and hairless. What causes the smoothness of peaches? A graduate student in our team also noticed this interesting question. Based on the results of previous genetic studies, he found the key candidate gene that causes the differentiation between hairy peaches and nectarines after more than a year of gene function analysis and verification.

Just when he was happily preparing to write an academic paper, a similar article was quietly published online - an Italian scientist also paid attention to this problem and discovered the key gene that controls the formation of nectarines. The same traits, the same gene, meant that the student's scientific research work suddenly became unattractive. While comforting the lost student, I was thinking about how to conduct more in-depth research in this area so that the previous efforts would not be in vain, and I also looked forward to providing more conclusive evidence for understanding the differentiation mechanism of nectarines and peaches.

Hard work pays off. With the joint efforts of team members, we have further found the reason for the shiny surface of nectarines based on the hairy and hairless surfaces of peach fruits. What's more interesting is that the gene that controls these two traits is the same - PpMYB25 . This gene not only controls the formation of peach skin hairs, but also regulates the synthesis of skin wax. Therefore, if PpMYB25 mutates, it will lead to the shiny and hairless characteristics of peach skin, which is what we usually call "nectarines".

Part.4 "Light makeup" or "heavy makeup"? Anthocyanins have the final say

In addition to peach fruits, people's love for peach blossoms has been increasing since ancient times, and the two-color peach is the undisputed leader among peach blossoms. "A cluster of peach blossoms blooms without an owner, I love deep red and light red" and "Luckily I know your peach face, and from now on there will be more warm spring on the roads." The Song Dynasty poet Shao Yong also wrote a poem to praise the two-color peach, "Both red and pink are good, and their beauty is different. I wonder if they are the twin sisters in the palace, and they are willing to marry the spring breeze at the same time." The two-color peach is commonly known as the "red and white flower" peach. This variety has alternating red, white and pink flowers on a tree or a branch, and some petals are even red and white.

In order to understand the magical phenomenon of "jumping colors" in red and white flowers, we conducted a lot of research: from the analysis of the difference in anthocyanin content and types in flowers of different colors, to the detection of the transcription level of structural genes and anthocyanin transporters in the anthocyanin synthesis pathway; from comparative transcriptome analysis to comparative proteome analysis... Behind each seemingly simple process, there are countless days and nights of hard work by team members, and repeated efforts. As the research continues to deepen, we finally figured out the reason for the production of this variegated flower.

It turns out that the Riant gene that controls the transport of anthocyanins in peach is rather "naughty". The study found that several bases were missing or inserted in white and pink flowers, which caused the Riant gene to become inactive, so anthocyanins could not be normally transported to the vacuole for storage , resulting in the difference in the color of peach flowers. In the whole plant, it will form a phenomenon that a tree, a branch or a flower can show red, white and pink at the same time.

Part.5 We are achieving this industry's "small goal" step by step

Color and flavor quality are two main factors in evaluating fruit quality. Among them, the content and ratio of organic acids and soluble sugars are the key factors that determine the flavor quality of fruits. In order to further improve the commercial value of peaches, our team has also been committed to studying the genetic mechanism of organic acid and soluble sugar accumulation in peach fruits. Chinese people prefer sweet taste, while European and American countries prefer sour taste. Based on this difference in taste, the East and the West also have different focuses in the selection and breeding of fruit tree varieties.

Some peach varieties bred by Chinese people are mostly "high sugar and low acid", while those in the West are "high sugar and high acid", or "medium sugar and high acid". The phenotypic differences between different varieties are certainly related to the level of planting technology and environmental factors, but this difference is mainly determined by genetic factors. In order to understand the mechanism that affects the acidity and sugar content of peach fruit, we have carried out relevant research. In the past decade, our team has conserved more than 200 core peach germplasm materials. Through these materials and with the help of genetic methods, we have identified candidate genes that control the acidity and sugar content of peach fruit, and clarified their mechanism of affecting the sugar and acid content in peach fruit.

Based on these research results, we have developed a series of molecular markers that are significantly associated with sugar and acid traits . Through these key site information, we can guide the selection of peach hybrid offspring and provide technical support for the selection and breeding of high-quality peach varieties. "The ultimate goal of basic research is to serve industrial development." Traditional breeding methods are gradually being replaced by modern breeding, and technologies such as whole genome selection breeding, genetic engineering improvement and gene editing will eventually come to the stage of the times due to their obvious advantages.

However, the genetic transformation of peach is a global problem, and so far there is no efficient and complete peach stable genetic transformation system. "Even if it is a hard bone, we have to gnaw it down." After five years of hard work, after trying more than 100 different varieties of different explant materials, we finally built a root genetic transformation technology system for peaches mediated by Agrobacterium rhizogenes , and obtained a composite plant of "transgenic roots-wild shoots". At the same time, we have also successfully established a stable genetic transformation system for peach callus tissue , and the construction of the transformation system for complete peach plants is currently in progress.

Part.6 When I encountered a bottleneck, I chose to "bury" myself in the literature

Many people ask me what is the secret to doing scientific research? I think about it, there is no secret, but if I have to say it, it is "perseverance". Whenever I encounter a scientific research problem or bottleneck, I will "bury" myself in the literature, think and analyze repeatedly, and look for a breakthrough to solve the problem. It is this attitude of constantly enriching myself with knowledge at the forefront of science, constantly observing the latest dynamic needs of the country and the industry, and constantly conducting experimental analysis and summary that enables us to make continuous progress in research.

Our research has not only achieved important academic breakthroughs, but also has far-reaching significance for the development of the peach industry. Based on the basic research results of peach flavor and color quality, we have developed molecular markers that are closely linked to the sugar and acid content, selected hybrid parents, and carried out molecular marker-assisted selection breeding. In the past two years, our team has cooperated with the Hubei Academy of Agricultural Sciences and the Anhui Academy of Agricultural Sciences to select and breed four new peach varieties, with a cumulative application and promotion area of ​​more than 20,000 acres. These new varieties not only enrich market choices, but also improve the economic benefits of the peach industry.

In the research on peach fruit genetics and improvement, we have encountered many challenges, but we have also made many important breakthroughs. In the future, we hope to achieve free regulation of peach color and flavor, strive to meet the diverse needs of consumers, and significantly enhance the competitiveness of the peach industry. We will continue to conduct in-depth research, strive to make more breakthroughs in the field of peach fruit genetics and improvement, and contribute to the development of the peach industry. Scientific research is a long and arduous task that requires unremitting efforts and innovative spirit. On the road of scientific research, we are like hard-working craftsmen, constantly working in the peach orchard, and cultivating batches of rising stars. However, we are all willing to be "pavers" and pass on this enthusiasm for scientific research from generation to generation...

Source: Science Institute